1. Field of the Invention
The present invention relates to a variable valve lift apparatus of an engine for a vehicle, and more particularly to a variable valve lift apparatus of an engine for a vehicle that can continuously vary a valve lift height.
2. Description of Related Art
Generally, a combustion chamber, in which fuel burns, is formed in an engine so that a vehicle can generate power. A valve train including an intake/exhaust valve that can control intake air and exhaust gas is disposed adjacent to the combustion chamber. The valve train opens and closes the combustion chamber by a crankshaft.
Generally, in such a valve train, a cam that has a regular shape lifts a valve as much as a predetermined lift amount, but the amount of the intake air or exhaust gas cannot be variably controlled.
Accordingly, when the valve train is designed according to a low speed driving condition, the timing and period that the valve is opened is not enough to satisfy a high speed driving condition, and when the valve train is designed corresponding to a high speed driving condition, the opposite phenomenon occurs.
More specifically, when the general engine is tuned for a high speed, the valve lift is established larger, and thereby the engine has excellent performance at high speed but has problems satisfying idle stability and torque at low speed.
On the contrary, when the general engine is tuned for a low speed, the engine has excellent performance at low speed but has problems satisfying output at high speed. However, in a variable valve lift apparatus, the valve lift can be variably controlled corresponding to a high or low speed, and so more advantages at low and high speed can be obtained.
Recently, techniques for improving charging efficiency as well as multi-valves for improving fuel consumption and output power have been developed. As a result, a variable induction system (VIS) in which a length or cross-section of the intake manifold can be variably controlled in accordance with a rotation range of the engine so as to minimize the resistance of the intake air, a variable valve timing (VVT) apparatus for controlling opening timing and opening amount of the valve so as to vary the overlap timing, and a variable valve lift (VVL) apparatus have been developed.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.